A lighting fixture 100 having a ceiling frame structure as shown in FIGS. 7A to 7C is conventionally known for a clean room which is, for example, used in a manufacturing step or an inspection step of precision instruments or used at institutions and the like. A ceiling frame 101 comprised in the lighting fixture 100 has a structure such that an attachment portion 102 positioned at the upper end of the frame is suspended from the ceiling (slab) of a building, and lighting equipment 110 such as a fluorescent light 110a is attached to the bottom surface of a main frame 10, which is located at the lower portion of the ceiling frame, so that the lighting equipment 110 is protruded. Furthermore, in the step conducted after the lighting fixture 100 is attached to the ceiling, a power distribution cable 111 can be wired in a hollow portion 104, which is located within the ceiling frame 101 of the lighting fixture 100, in order to make it possible to provide a power supply to the lighting equipment 110.
A lighting fixture such as those described above is generally used so that the lighting fixture is attached to the ceiling of a building, and therefore, a frame having a reverse “T” shape as shown as the ceiling frame 101 in illustrated examples is used for the lighting fixture in order to enable the attachment of the lighting fixture to a ceiling with screws or the like.
The lighting fixture 100 as shown in FIG. 7A to 7C can be used in combination such that plural lighting fixtures are combined when it is attached to a ceiling, and for example, plural lighting fixtures are combined with a beam-like support to form a grid pattern. Furthermore, a screen panel, a HEPA (High Efficiency Particulate Air) filter unit, an air-conditioning system and the like, which are not illustrated in figures, can be set so that they are fit in between the lighting fixtures 100 and the beam-like support, which are set in a grid pattern, to form a ceiling system used in a room such as a clean room. Here, edges of the air-conditioning system or the like are mounted on a top surface 103a of the main frame 103.
However, the lighting fixture 100 such as those shown in FIG. 7A to 7C, which has been used in the conventional clean room, has a structure wherein lighting equipment 110 is protruded toward downward from a main frame 103, and there is a problem that the available floor height of a room is reduced. As a result, for example, space efficiency decreases when the lighting fixture is installed in a clean room where space is limited, and furthermore, a fluorescent lamp 110a may be broken by touching the fluorescent lamp with a user's body or an instrument, while various operations are being conducted in the clean room.
Furthermore, in order to secure predetermined available floor height in a clean room or the like while a conventional lighting fixture is used, it is necessary to construct a clean room so that height of the ceiling is increased according to the height of a protruded portion of the lighting fixture 100. Therefore, there was a problem in that construction cost increases. Furthermore, as a result of increasing the height of a ceiling, wasted space is generated in a clean room, and it is necessary to conduct circulation, air conditioning and cleaning of extra air, and therefore, running cost increases.
In order to overcome the aforementioned problems of conventional lighting fixtures and ceiling systems, new lighting fixtures and ceiling systems have been proposed. More specifically, a lighting fixture and system have been proposed wherein a storage recess which can store a luminaire is provided at a main frame of a ceiling frame, a luminaire equipped with a reflective umbrella and a fluorescent lamp is set in the storage recess, and an air introducing hole, which enables air to pass through the reflective umbrella, is provided to the main frame. (For example, Patent Document 1.)
In the lighting fixture having the ceiling frame structure described in Patent Document 1, the space efficiency of a clean room is not reduced since the luminaire is stored in the ceiling frame as described above. Furthermore, construction cost and running cost do not increase since it is not necessary to construct a building so that ceiling height of the room is increased. In addition, it is disclosed in the document that an air introducing hole is provided and air is introduced into the reflective umbrella via the hole, and such a structure prevents dust from covering a tube of a fluorescent lamp.
However, the lighting fixture described in Patent Document 1 has the following problems. One concrete example of a problem is that, when the aforementioned lighting fixture is installed, it is necessary for an electrician to attach a power distribution cable, which is supplied from the upper side of the ceiling such that it hangs down, to every ceiling frame suspended from the ceiling after the ceiling is constructed. Such an attachment requires a lot of work. Furthermore, another concrete example of a problem is that, while the aforementioned power distribution cable is attached to each ceiling frame as feed wiring, it is necessary to strip the end cover of the cable, to connect the stripped cable with a terminal board of each apparatus for a fluorescent lamp, and to attach a fluorescent lamp to each apparatus one by one. Therefore, it is difficult to reduce construction time.
Furthermore, after installing and attaching a lighting fixture, it is necessary to exchange the fluorescent lamps approximately every two years for a clean room, although the frequency varies according to the irradiation time of the luminaire. However, the ceiling frame described in Patent Document 1 has a structure wherein a fluorescent lamp is set in the narrow ceiling frame, and the workability at the time of exchanging a fluorescent lamp is poor. Therefore, there is a problem in that increased work and increased cost are required when maintenance is conducted.
Moreover, since the ceiling frame of Patent document 1 has a structure wherein the air introducing hole is provided as described above, there is a problem in that a fluorescent lamp, a power supply and the like may suffer harmful effects such that a lot of dust may enter the main frame, although such a structure can prevent dust from covering a tube of a fluorescent lamp.    Patent documents 1: Japanese Patent No. 3562602